Watch crystal



y 3 1934- HE. LINDHE 1,964,886

WATCH CRYSTAL Filed Jan. 24, 1930 Hen/7 E L indbe Arm/way.

Patented 3, 1934 WATCH CRYSTAL Henry E. Lindhe, Chicago, 111., assignor to Bakelite Corporation, New York, N. 1., a corporation of Delaware Application January 24, 1930, Serial No. 423,003

4 Claims.

This invention relates to watch crystals and similar protective transparent coverings made of non-vitreous materials and commonly referred to as non-breakable.

In response to a demand which has arisen for non-breakable watch crystals, celluloid materials, that is, compounds of cellulose suitably plasticized, have come into use to some extent for this purpose. Watch crystals made of celluloid ma terials, however, are found in practice to be objectionable in that they are readily bent to thereby interfere with the movement of the hands, particularly as they tend to soften at body temperatures, they are easily scratched and they gradually change to an ugly yellow color with use. A well recognized objection is the shrinkage that occurs with time, and seasoning for long periods covering years does not cure this serious defect.

'According to the present invention watch crystals and similar articles of the non-breakable type are provided that are superiorto those heretofore supplied in that they are not readily bent or scratched, are substantially free from any apparent discolorationupon aging and do not soften at body temperatures. In addition watch crystals made in accordance with this disclosure do not shrink, but on the contrary exhibit a most useful property of becoming more tightly secured in a bezel with increasing use.

These objects of the invention are secured by the use of transparent materials of a heat-hardened synthetic resinous type, and more particularly materials of this character which result from the reaction of a polyhydric alcohol, such as glycerol, with a polybasic acid, such as phthalic anhydride, and which are for convenience designated as alkyd resin. Alkyd resins are commercially procurable which have the property of remaining hard 'at body temperatures but which soften to the extent that they can be manipulated or deformed whensubjected to materially higher temperatures, that is, about 400 F. Such resins can be prepared, for example, in accordance with the disclosure of a patent to Schmidt, No. 1,739,- '7'l1 granted December 17, 1929. It is this property of alkyd resins that is particularly useful in yielding tight-fitting crystals since plates of the material that are deformed at elevated temperatures normally show a tendency to return to their original condition. I

In order that the invention may be completely understood attention is directed to the accompanying drawing in which Figure 1 shows in perspective an assembly of dies and a plate to be molded or shaped shown in spaced relation; Figure 2 is a side-view of a molded plate; Figure 3 is a top view of a molded plate out to size; Figure 4 is a transverse section of the plate on the line H of Figure 3; Figure 5 illustrates an assembly of a bezel and a molded crystal secured in a clamp; and Figure 6 is a'sectional view of another form of apparatus for manufacturing crystals.

Glyptal resinoids in the form of plates or rods are first sliced into thin plates of about 1 millimeter or so in thickness. These plates are then shaped between dies to obtain the proper domed efiect and out to the desired contour. Such a domed eifect can be secured by theme of dies as illustrated in Figure 1 comprising a. bottom mem- 79 her 11 having upstanding guides .12 and a domed center 13 of the desired configurationp For co operation with the member 11 there is provided a top member 14 that has its center portion removed to accommodate the dome 13 and is adapted to fit within the guides 12. A thin plate section 10 of resin having been heated until the softening point is reached, that is, about 400 F., is placed between members 11 and 14 and the assembly is then subjected to pressure by-means 8% of a screw clamp or other suitable device. It is then set aside and allowed to cool to room temperature or below its softening point after which theclamps are removed; cooling may be hastened by quenching the work in water.

A resinous plate that has been domed in this manner, as shown in Figure 2, is then out or blanked by dies to the proper crystal size or so that it will fit loosely into the metal bezel for which it is intended. The crystal can be edged to be somewhat larger than the bezel to which it is to be fitted; in this case it can be snapped into the groove of the bezel and. is ready for use.

As the slicing operation producing the thin plates generally results in a rough or non-transparent surface, it becomes necessary to polish the surfaces of the crystal; this step is preferably performed after the crystal is otherwise finished, but

it can be done at any stage in the crystal manufacture. Prior to its insertion in the bezel the 100 edge 15 can be rounded, either by grinding or'by a suitable design of the blanking dies, to give what is known as the 1enti1e'eflect whereby a close and dust-tight contact with the groove of the bezel is made possible. I

The finished crystal when smaller than the bezel is mounted by clamping the assembly 01! the two between brass blocks 16 and 1'7 as shown in. Figure 5, andpressure is applied by means of a screw clamp '18, which pressure may be transmitted to one of the blocks 16. through the medium of a spring 19. The assembly is heated until the crystal begins to soften, whereupon the pressurev applied on the crystal causes some flattening of the dome and forces the crystal firmly into the under-cut groove of the bezel. After cooling the clamp is removed.

It is obvious that the steps above outlined can be modified and their order changed. For example the crystals may be cut or punched to approximate sizes. or contoursprior to or simultaneously with a doming operation. A simultaneous operation is secured with a compound die illustrated in Figure 8. A movable plunger die 20 cooperates with a fixed blanking die 21 whereby a crystal of the same peripheral contour as the plunger can be cut from a plate 10 placed between them. The end of the plunger is domed to act as a forming die and a cooperating forming or doming die 22 is mounted in the fixed die opening. A spring 23 maintains the forming die 22 above the surface of the fixed die. As a result when the descending plunger contacts the heated plate 10 the plate is given a domed formation by the punch 20 and die 22 and further movement of the punch depresses the die 22 against the action of the spring below the fixed die surface so that the punch coacts with the die to cut the crystal from the plate. One downward stroke of the plunger therefore domes, blanks and .cools the crystal (due to absorption of heat by the metal dies), and upon raising the plunger the crystal is ejected through the action of the spring 23.

Crystals made in accordance with the above procedure have the advantage that they need only approximate in size and shape the bezels into which they are to be mounted. If a domed crystal is somewhat smaller than the bezel the application of heat and pressure, as above described and illustrated in Figure 5, causes the crystal to fiatten and thereby fit firmly into the bezel. The domed crystal may as above stated be machined so that it can be snapped into place. Or it may, 4

however, be so much larger than the bezel that it is preferable to place a crystal within the bezel and force it toward the normally exterior side of the bezel until it springs into'the bezel groove; in other words the assembly is then the reverse of that shown in Figure 5, the block 16 contacting the concave side of the crystal and a suitable ring being provided to support the bezel on the block 17. From this the fact is apparent that the crystals need only be approximate in size which gives greater latitude with a smaller selection of crystals than is at present possible with glass crystals and the manner of mounting yields a dust-proof fit.

I claim:

1. Watch crystal of the non-breakable type comprising an alkyd resin prepared by the reaction of a polyhydric alcohol and a polybasic acid and characterized by hardness at body temperature but softening at materially elevated temperatures.

2.. Watch crystal of the non-breakable type comprising an alkyd resin prepared by the reaction of a polyhydric alcohol and a polybasic acid and characterized by hardness at body temperature but softening at temperatures of about 400 F.

3. The combination with a bezel of a crystal comprising an alkyd resin prepared by the reaction of a polyhydric alcohol and a polybasic acid and characterized by hardness at body temperature but softening at materially elevated temperatures.

4. The combination with a bezel of a domed crystal comprising an alkyd resin prepared by the reaction of a polyphydric alcohol and a polybasic acid and characterized by hardness at body temperature but softening at materially elevated temperatures.

HENRY E. LINDHE. 

